Electric power steering apparatus

Abstract

A torque detection portion includes a first arm having a detection coil L 1 and a resistor R 1 , and a second arm having a detection coil L 2 and a resistor R 2 . When a test mode is set, a reference voltage V ref having an abnormal value is outputted to a monitoring portion 13 . An abnormal condition is intentionally caused in the monitoring portion 13 . A main torque signal V tm is compared with a sub torque signal V ts in the monitoring portion 13 . When the reference voltage V ref set in the monitoring portion 13 has the abnormal value, a sub torque signal V ts having a level of 0 (V ts =0) is forcibly outputted in a normal condition. Then the signal V tm is equal to the signal V ts , the monitoring portion 13 determines that a shortcircuit occurs between a main torque signal line and a sub torque signal line.

1. An electric power steering apparatus, comprising a torque detection unit comprising:
 a torque detection element comprising a pair of detection coils of which impedances change in accordance with torque; 
 a torque detection portion comprising a monitoring portion which monitors the torque detection element; and 
 a shortcircuit failure detection portion which detects a shortcircuit failure occurring between a main torque signal line and a sub torque signal line of the detection coils, wherein 
 the shortcircuit failure detection portion detects the shortcircuit failure occurring between the main torque signal line and the sub torque signal line by comparing a main torque signal and a sub torque signal, which are outputted from the torque detection portion when an abnormal condition is intentionally set in the monitoring portion. 
 
   
   
     2. The electric power steering apparatus according to  claim 1 , wherein the torque detection unit further comprises a reference voltage generation circuit which outputs a particular reference voltage, which differs from a standard reference voltage, to the monitoring portion and
 when a test mode, in which a torque detection circuit is tested, is set, the abnormal condition is intentionally set in the monitoring portion by setting the particular reference voltage therein. 
 
   
   
     3. The electric power steering apparatus according to  claim 2 , wherein the particular reference voltage, which is set in the monitoring portion when the test mode is set, exceeds the standard reference voltage. 
   
   
     4. The electric power steering apparatus according to  claim 1 , wherein the monitoring portion is configured so that when an abnormal condition is set therein by intentionally setting the particular reference voltage therein, the sub torque signal line is grounded. 
   
   
     5. The electric power steering apparatus according to  claim 1 , wherein the shortcircuit failure detection portion determines that the shortcircuit failure occurring between the main torque signal line and the sub torque signal line occurs in a case where a test mode is set, where an abnormal condition is set in the monitoring portion by setting a particular reference voltage exceeding a standard reference voltage therein, and where a main torque signal voltage and a sub torque signal voltage outputted from the torque detection portion are equal to each other. 
   
   
     6. The electric power steering apparatus according to  claim 1 , wherein when the shortcircuit failure is detected, the torque detection unit changes a mode thereof into a fail safe mode.